The present invention relates generally to recovery of acid soluble copper by extraction from copper-containing ores. More specifically, the present invention provides a process for extracting copper using spent acidic cupric chloride etchant solution from printed wire board manufacture as a raw material source of copper and acid using standard solvent extraction (SX) and electrowinning (EW) processes.
Copper is obtained by mining acid soluble copper-containing ore and piling the collected ore into a heap at the surface of the mine. Copper refining to produce high quality copper cathode is generally carried out in three steps known as acid leaching, followed by solvent extraction (SX) and then electrowinning (EW).
In the acid leaching step, an acid leach solution, generally sulfuric acid, is sprayed over the heap so that the leach solution flows through the heap dissolving copper in the ore and forming a copper-containing solution (copper sulfate). The copper laden solution, collected at the bottom of the pile, contains approximately 0.5-15 g/L, copper more usually 1-5 g/L copper, and is called (acidic) pregnant leach solution (PLS).
PLS is transferred to the SX process, which utilizes a liquid organic based ion-exchange extractant, selective for copper, in a solvent that is substantially immiscible in the aqueous solution. The PLS and copper depleted organic extractant phase (commonly referred to as the barren organic phase) are typically mixed together in a large agitated tank and then transferred to a settler where the pregnant or copper loaded organic and barren or copper depleted aqueous phases are allowed to separate to form an upper copper-loaded organic phase and a lower copper-depleted acidic aqueous raffinate phase. The lower aqueous raffinate phase is removed from the settler and is typically recycled and used as a leachant again to leach copper from the ore in the heap.
The loaded organic phase is transferred to a second mixer and mixed with acidic lean electrolyte which is obtained from a downstream EW plant. The mixture is transferred to a second settler and the organic and aqueous phases are allowed to separate. The lean electrolyte (25-45 g/L copper, for example 30-40 g/L copper), which is typically a highly acidic sulfuric acid stream, extracts the copper from the loaded organic phase and forms a rich copper electrolyte aqueous phase. The copper rich electrolyte (55-80 g/L, for example 60-70 g/L copper) phase is transferred to the EW plant to produce the copper cathode final product. Depleted electrolyte from the EW plant, termed lean electrolyte, is recycled and mixed with the loaded organic phase again in the mixer and settler to extract the copper from the loaded organic phase. In the mixer/settler operations, the loaded organic phase, after contact with the lean electrolyte becomes depleted of the extracted copper, and this organic phase is typically termed the stripped or barren organic phase, and this phase is typically recycled to the first mixer to contact and extract copper from new PLS.
A need exists for improving the SX process for extracting copper with reduced cost, reduced mine waste and better utilization of capital and raw material resources. The present invention seeks to fill that need.
It has now been discovered according to the present invention that it is possible to improve the yield of copper without additional ore mining and with little capital expense while at the same time reducing purchased sulfuric acid use. The present inventor has discovered surprisingly that it is possible, in a SX-EW process, to obtain improved recovery of copper using spent acidic cupric chloride etchant solution from printed wire board manufacture as a source of copper and acid. The copper present in the spent acidic printed wire board etchant is also recovered, thereby increasing the overall yield of copper in the SX-EW process, whilst the presence of hydrochloric acid in the spent cupric chloride etchant reduces the amount of additional purchased sulfuric acid required which must be added to the leaching process, thereby reducing costs.
In one aspect, the present invention provides a process for the recovery of copper from a copper containing source by SX-EW, wherein a PLS obtained by acid leaching a copper-containing source, is mixed with aqueous acidic cupric chloride to produce a copper-containing SX-EW feedstock for the production of copper cathode.